1. Field of the Invention
The present invention generally relates to a moving position detector. More particularly, the present invention relates to a rotational position detector which utilizes magnetoelectric transducers having particular saturation characteristics as to voltage output, such as magnetoelectric transducer elements composed of a ferromagnetic material, e.g., Ni-Co type alloy and Ni-Fe type alloy (hereinafter referred to as "MR elements"), and nonlinear type Hall elements.
2. Description of Related Art
A rotational position detector in which the outer periphery of a rotor has a magnetized surface alternately provided with different magnetic poles and the magnetized surface is detected by using a rotational angle sensor utilizing magnetoelectric transducers has been proposed as disclosed, for example, in Japanese Unexamined Patent Publication No. 54-156656, Japanese Unexamined Utility Model Publication No. 56-12815 or Japanese Examined Patent Publication No. 2-52966.
The rotational angle sensor of the above rotational position detector comprises a single or a plurality of magnetoelectric transducers to obtain the output voltage from the rotational angle sensor by means of the magnetoelectric transducing action according to the magnetic field intensity. On the other hand, the magnetized surface of the rotor is alternately provided with different magnetic poles and a reference position part magnetized with a larger magnetization pitch is formed in part of the magnetized surface so that the rotational angle sensor generates rotational angle signals and reference position signals. Furthermore, the waveform of the output signal from the rotational angle sensor is shaped, and the rotational angle signal is generated according to the reference position signal. During this process, the output voltage from the magnetoelectric transducer becomes constant (e.g., at "0" value) in the reference position part for the specified duration, and consequently the reference position signal can be obtained.
However, in the rotational position detector in the above arrangement, when the magnetization pitch of magnetic poles is widened as shown in (A) of. FIG. 17, the magnetic field intensity in the reference position part lowers at the central part thereof as shown in (B) of FIG. 17. As a result, a swell or fluctuating noise as shown in (C) of FIG. 17 is present on the output voltage signal from the rotational angle sensor in the reference position part according to the variation in the magnetic field intensity.
In addition to the above problem, when ferromagnetic MR elements composed of a ferromagnetic material, such as a Ni-Co type alloy, are used as magnetoelectric transducers, there are the adverse effects of the hysteresis characteristics as to the output voltage Vm in the range A of magnetic field intensity Hy as shown in FIG. 16. Moreover, the hysteresis characteristics themselves vary according to the material manufacturing conditions, i.e, the hysteresis characteristics differ from product to product. This makes the output waveform in the reference position part more unstable.
For these reasons, the reference position detecting precision is lowered. Therefore, when the conventional rotational position detector is used in an operational environment or rotation which is subject to a large variation or to high,precision high-volume pulses, such as rotational position detectors for automobile engines, these problems may severely restrict the design of rotational angle sensors.